[We all get trivia clogging our inboxes. Some items are more trivial than others. This was one of the more illuminating examples, found this Labor Day on the Scouts-L listserv. -- DLA]
It's a holiday, so I thought I might just list a few things for consideration.
There - a place away
Their - possessive; it belongs to them
They're - contraction; 'they are'
Its - possessive form of 'it' (his, hers its - no apostrophe)
It's - contraction; 'it is' or ' it has'
Your - possessive form of 'you' (It belong to you)
You're - contraction; 'you are'
Yore - long ago, as in 'days of yore'
An - singular article, used before a vowel (an accident) or silent consonant (an historical event)
And - conjuntion; connects two items (peace and joy)
Pros - pural for (opposite of cons [against]; pros and cons)
Pros - plural of pro (short form of 'professional') [no apostrophe]
Pro's - possessive; belongs to the pro
Prose - written word; not poetry ;-)
Where - a place unspecified or unknown
Wear - to have on clothing
Were - 3rd person plural past tense of 'to be' (They were....)
We're - contraction; 'we are'
Know - to be mentally aware of something ('I know the rules.')
No - negative interjection ('No, I don't have it.')
Want - to desire
Wont - enjoy, take pleasure in (usually pronounced the same as 'want').
Won't - contraction of 'will not.'
Lose - ('looz') to part with, to cease to have
Loose - ('looss') freedom from restraint, untied or unbound
Do - perform, execute, bring about
Due - directly ('due north'); attributed, ascribable ('due to....')
Affect - (v) to influence ['affect the outcome']
Effect - (n) appearance ['a special effect']; (v) to accomplish ['effect a change in the rules.']
Cloth - (n) pliable material, usually knitted, woven, or felted ['clawth']
Clothe - (v) act of putting on clothing, to dress [clOthe]
Advice - (n) recommendation [ad-vice]
Advise - (v) to give advice, to counsel [ad-vize]
Lie - (n) an untruth; (v1) to tell an untruth; (v2) to recline, to rest [past tense: lay, have lain; e.g. "When did you lie down?' 'I lay down yesterday for a quiet nap.']
Lay - (v) to put, to place [past tense: laid, have laid; e.g. 'Where did you lay the book?' 'I laid it on the table.']
Preventative - poor spelling; see 'Preventive'
Preventive - concerned with prevention, precautionary
Plural form - usually add 's' (not 'apostrophe s') [same for abbreviations, e.g., 'PL' and 'PLs']; if word ends in 'ch,' 'x,' 's,' or 's-like' sounds add 'es'; if word ends in 'y,' drop the 'y' and add 'ies'; for plural names or hyphenated words, pluralize the primary word, e.g., court of honor becomes courts of honor, mother-in-law becomes mothers-in-law.
Questions? I highly recommend http://grammar.ccc.commnet.edu/grammar/